This JPL Rapid Mission Architecture (RMA) study was not a mission concept study of a single mission, but instead was an architectural-level study of a set of missions to the Neptune system and, for some, continued travel to a Kuiper Belt Object (KBO). It was commissioned by three Planetary Science Decadal Survey Panels: Giant Planets, Satellites, and Primitive Bodies, whose diverse sets of science priorities made tailoring architectures to the science priorities particularly challenging. The panels' intent is to use the results to compare key metrics of the architectures (including science value, cost, and risk) and decide which ones, if any, merit individual, more detailed study. The study science team, with members from each of the panels, emphasized lower-cost missions (e.g., potential candidate New Frontiers class missions or lower-cost flagship missions). As a result, a large fraction of both the science objectives and the selected architectures favor missions requiring the fewest resources.